1. Technical Field
This invention relates to sewage treatment plants and, more particularly, to systems for use in such plants which utilize a series of generally concentric channels or tanks through which treated sewage progresses inwardly from tank to tank during digestion, aeration and clarification as the treatment process is carried out.
2. Background Information
As the sewage being treated in systems of the foregoing type is agitated and aerated in outer ring-like tanks of the system in an orbiting or circular flow pattern, it also migrates inwardly through passages in the tank walls toward the center of the system, eventually finding its way to a centermost quiescent zone or clarifying tank in which sludge is allowed to precipitate out onto the bottom of the tank while the clarified effluent is allowed to overflow into discharge weirs. The sludge must be continuously removed from the bottom of the clairfying tank, yet in a way which does not unduly disturb or agitate the contents and interface with clarification. Thus, a common practice is to suspend a sludge siphon header into the tank and move it very gently and slowly along the bottom in an orbiting path of travel. Powered prime movers such as engines and motors, along with gears and associated drive trains have typically been utilized for slowly driving an overhead bridge to which the siphon header is attached in an orbiting path of travel to provide the slow, steady movement of the header. However, such motors and gears are inherently expensive and troublesome, requiring not only a substantial initial capital outlay but also significant expenditures from time-to-time for maintenance and repair.